胶东和鲁西金矿床空间分布分形差异及对金来源的启示

The spatial distribution differences between Jiaodong and Luxi terrane gold deposits by fractal method and its implications for the source of gold

胶东和鲁西地体发育大量的中生代金矿床,其金元素的来源一直是学术界争论的焦点,可能的来源方式为:交代岩石圈地幔、前寒武纪变质基底和中生代二长花岗岩。为了进一步厘定金的来源,文章从金的富集阶段模式和金矿床是金元素超常富集地质体的思想出发,运用金矿床的空间分布数据和空间分析的分形地质统计方法,进行了研究。研究结果发现,胶东金矿床(N=823)具有一阶段的空间分形分布模式,其分形维数α=0.726,具有单一来源或单一成因的特征;结合前人研究和克拉通破坏和西太平洋俯冲的地质背景,推断胶东金元素极有可能是单一的交代岩石圈地幔来源;而胶东地体西侧鲁西地体中发育的金矿床(N=139)则具有二阶段的空间分形分布模式,其分形维数分别为α_(1)=1.630和α_(2)=0.850,具有2种金元素来源或2种成因类型的特征,可能分别对应着早前寒武纪变质岩及韧性剪切带有关金矿床和晚中生代岩浆活动有关金矿床空间分布的分形维数,后者的值与胶东地体的分形维数相近,结合前人研究,推测鲁西部分金矿床来源于交代岩石圈地幔的贡献,另一部分则可能来自于花岗质岩浆。

A large number of Mesozoic gold deposits are developed in Jiaodong and Luxi terranes of Shandong Province,E China,and the sources of the gold elements have been the focus of scholars debate,which may be metasomatic lithospheric mantle,Precambrian metamorphic basement and Mesozoic monzogranite.In order to further determine the origin of gold,this paper studies the spatial distribution data of gold deposits and fractal geological statistics method based on the model of gold enrichment stages and the idea that gold deposits are supernormal enrichment geological bodies.The results show that the Jiaodong gold deposit(N=823)has a one-stage spatial fractal distribution pattern,and its fractal dimensionα=0.726,which is characterized by a single source.Combined with the geological background of the craton destruction and the subduction of the Western Pacific plate,it is inferred that the gold element in Jiaodong gold deposits is probably a single metasomatic lithospheric mantle source.However,the gold deposits(N=139)developed in the Luxi terrane have a two-stage spatial fractal distribution pattern,and their fractal dimensions areα_(1)=1.630 andα_(2)=0.850,respectively.The latter value is close to the fractal dimension of the Jiaodong terrane,indicating that the gold element in Luxi gold deposits is partly contributed by metasomatic lithospheric mantle,the other part may come from the reactivation of granitic magma.